Explain the steps of converting food into energy.

There are four steps to convert food into energy:

a) Ingestion, mastication and swallowing : Ingestion or taking in of food and mastication are done by mouth and teeth with the help of the tongue. The pharynx and oesophagus help in swallowing.

b) Digestion : Takes place in the stomach and upper part of the small intestine.

c) Absorption : Food is absorbed in small intestine. Water is absorbed in the large intestine.

d) Excretion : Large intestine helps in excretion of residue in the form of faeces or stool.

Additional organs help in the process of digestion : Salivary glands supply saliva. Liver supplies bile. Bile salts play important role in fat digestion. Pancreas secretes insulin from islets of langerhans. Insulin helps the tissues to use sugar for energy.